Question

Consider a class with 100 enrolled students. None of the students were ill at the beginning of the school year. On September 30, a total of five students reported having gastroenteritis. All continued to be ill on October 1 but all five recovered in 3 days. On October 14, another three students developed gastroenteritis. All of these students continued to be ill on October 15, but all three recovered 5 days later. In this example, assume that a person cannot get gastroenteritis more than once.
A. Calculate the pre-valence of gastroenteritis in the class on October 1.
B. Calculate the pre-valence of gastroenteritis in the class on October 30.
C. Calculate the cumulative incidence of gastroenteritis in the class during the month of October.

Answer 1

Answer:

A. Calculate the prevalence of gastroenteritis in the class on October 1.

• 5%

B. Calculate the prevalence of gastroenteritis in the class on October 30.

• 0%

C. Calculate the cumulative incidence of gastroenteritis in the class during the month of October.

• 3.16%

Step-by-step explanation:

Prevalence is calculated using the following formula:

(number of sick people / total number of people measured) x 100%

October 1 = (5 / 100) x 100% = 5%

October 30 = (0 / 100) x 100% = 0%

Cumulative = [3 / (100 - who got sick on September)] x 100% =  (3/95) x 100% = 3.16%

Since 5 students got sick during September, they cannot be included in the cumulative statistics for October. This means that the cumulative denominator will be 95, not 100.

Answer 2

A) The pre-valence of gastroenteritis in the class on October 1 is; 5%

B) The pre-valence of gastroenteritis in the class on October 30 is; 0%

C) The cumulative incidence of gastroenteritis in the class during the month of October = 3.16%

Formula for pre-valence is given by;

Prevalence = number of people with disease/number of people in the defined population.

We are given;

Number of people in class = 100 students

Number of people with the sickness on September 30 and October 1st = 5 students

Number of people with the sickness on October 14th = (5 - 5) + 3 = 3 students

All 3 students recovered 5 days after October 15th. Thus,

On October 20th;

Number of students with sickness = 0

Since no one can have it more than once, then;

On October 30th;

Number of students with sickness = 0

A) The pre-valence of gastroenteritis in the class on October 1 = 5/100 = 5%

B) The pre-valence of gastroenteritis in the class on October 30 = 0/100 = 0%

C) We want to calculate the cumulative incidence of gastroenteritis in the class during the month of October.

Since at end of September, 5 had the sickness, then the total we will be working with at end of October is; 100 - 5 = 95 since no one can have the sickness more than once.

Thus, cumulative incidence at end of October since only 3 people contacted it in October = 3/95 = 0.0316 or 3.16%

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